While I don't expect this to be accepted, I think it can start a discussion around supporting it.

There is a movement in recent languages to let YES/NO express TRUE/FALSE. Objective C, CoffeeScript and markup languages like YAML are some examples of that. I thing it works really well for ruby scripts, used as configuration files. The rails config/* files seem like great candidates for YES/NO usage.

Implementation wise, I choose to go with TRUE/FALSE like constants, rather than extra yes/no keywords as it seemed to me like the most unobtrusive way to introduce those.